Just to add to this discussion:
I have had shareware/trialware offered since 1996. I went to a lot of effort to combat piracy. One approach I used was to add code to a program to perodically "phone home" with registration information. Then I spent a lot of time checking on the various piracy sites (or warez sites as they are often called) - with a little effort, they are not hard to find - looking for pirated copies of my software and the registration info these were using. The "phone home" routine was buried deep in the program so would not be obvious to a hacker since the program (CyberSpyder Link Test) made extensive use of the internet - the call home would not be obvious. My home site contained a file of the known pirated registration info. The call home would compare the programs registration info with the known pirated info - on a match the pirated program was returned to "trial status". A hacked version that tried to bypass the normal registration check would end up calling home with a different code since the registration process also invoked some non-obvious other code changes.
What I discovered was that, in spite of a lot of pirated copies being available, very few were actually ever used so I became convinced that trying to trap these was not really worth the effort. I also realized that anyone who would actually use pirated software was unlikely to be a buyer anyway - they might play with a program a bit if they got it for free, but would not be a really serious ongoing user. I suspect the same is true of most users of pirated software. In many cases, the number of pirated programs is some kind of status symbol ("I have 3,579 programs/apps, how many do you have?") and the programs are not really being used.
Yes, there are a lot of pirated apps out there (check
http://thepiratebay.se/ and do a search for "android apps games" - it comes up with lot) but I don't think it is worth an extreme effort to try to prevent this because you will not likely succeed. Make reasonable efforts to ensure your apps are licensed but don't waste a lot of time trying for something that is totally foolproof - it is a basically a wasted effort and not worth the time.